Single base, self-igniting fluorescent lamp

ABSTRACT

A fluorescent lamp having a tubular glass envelope with a base attached to only one end and a flat seal or dome seal at the other end. A single mount structure is sealed within the envelope at the base end and comprises a first electrode supported at the base end, a lead-in wire connecting the first electrode to the base, a rigid glass tube projecting from the base end toward the flat seal end, a second electrode supported by the glass tube at the flat seal end, a lead-in wire passing coaxially through the glass tube to connect the second electrode to the base, and an ignition coil with an emissive coating connected between the electrodes and suspended away from the arc discharge path by support wires projecting from the glass tube.

[451 Nov. 19, 1974 1 1 SINGLE BASE, SELF-IGNITING FLUORESCENT LAMP [75] Inventor: William J. Roche, Merrimac, Mass.-

[73] Assignee: GTE Sylvania Incorporated,

Danvers, Mass.

[22] Filed: Dec. 5, 1973- [21] ApplQNo; 421,980

[52] US. Cl 315/46, 313/109, 313/238 [51] Int. Cl. H0lj l/88 [58] Field of Search 313/1, 109, 198, 238;

315/46, 49, 41, DIG. 5

[56] References Cited UNITED STATES PATENTS 2,344,122 3/1944 Bay et al... 315/49 2,930,934 3/1960 Wainio et al. .1 315/46 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Darwin R. Hostetter Attorney, Agent, or Firm-Edward 1. Coleman 57 ABSTRACT A fluorescent lamp having a tubular glass envelope with a base attached to only one end and a flat seal or dome seal at the other end. A single mount structure is sealed within the envelope at the base end and comprises a first electrode supportedat the base end, a lead-in wire connecting the first electrode to the base, a rigid glass tube projecting from the base end toward the flat seal end, a second electrode supported by the glass tube at the flat seal end, a lead-in wire passing coaxially through the glass tube to connect the second electrode to the base, and an ignition coil with an emissive coating connected between the electrodes and suspended away from the arc discharge path by support wires projecting from the glass tube.

9 Claims, 3 Drawing Figures SINGLE BASE, SELF-IGNITING FLUORESCENT LAMP BACKGROUND OF THE INVENTION ture installation. Such a lighting package has found uni-.

versal acceptance in applications where economy of space is not critical and where high illumination levels warrant reflectorized fixtures. In instances where space is at a premium or where modular simplicity is desired, such as in appliance lighting,'the conventional fluorescent lamp system loses its appeal.

The present invention overcomes these less desirable aspects of fluorescent lighting by incorporating all the electrical connections at one end of the lamp and providing an internal starting mechanism for the lamp. These features allow a fluorescent tube to be used in places not practical or flexible with existing fluorescent lamps.

A previous US. Pat. No. 3,753,036 of the present inventor, and assigned to the present assignee, describes an integrated fluorescent lamp unit having a single screw-in base at one end of a tubular envelope, a starting circuit of discrete electrical components contained in the lamp base, and a resistance wire ballast wound about the exterior of the lamp envelope. This patented lamp, which is primarily intended for DC operation,

provides one approach for filling the gap in available fluorescent lighting systems.

The present invention, on the other hand, provides a single base fluorescent lamp which is suitable foreither AC or DC operation and provides all the electrical contacts at a single end without recourse to exte'rnal wiring running along the sides of the lamp envelope. Further, a self-igniting feature is provided without resort to discrete circuit components either external or internal to the lamp.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved fluorescent lamp unit.

A principal object is to provide a fluorescent lamp which is self-igniting and has all connections at a single end of the lamp envelope.

Briefly, these objects are attained in a fluorescent lamp comprising: an hermetically sealed, tubular glass envelope having an internal phosphor coating and containing mercury and a rare gas; a base attached to one end of the envelope; and a single mount structure sealed in the base end of the envelope. The mount structure comprises a first electrode supported at the base end of the envelope, a lead-in wire connecting the first electrode to the base, a rigid insulating tube within the envelope projecting from the base end toward the other end of the envelope, a second electrode supported by the insulating tube at the other end of the envelope, a lead-in wire passing through the length of the insulating tube to connect the second electrode to the base, and an ignition coil having an emissive coating over substantially its entire length connected between the first and second electrodes and suspended away from the arc discharge path by support means projecting from the insulating tube.

The length of the lamp may be increased by employing a V-shaped ionization coil structure approximately midway along the length of the ignition coil.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully described hereinafter in conjunction with the accompanying drawings, in

which:

FIG. 1 is an elevation, partly in section, of one embodiment of a single-base fluorescent lamp according to the invention;

FIG. 2 is a volt-ampere characteristic curve, together with a portion of the ballast load line, of a typical lamp made according to FIG. I; and

FIG. 3 illustrates an alternative mount structure for the lamp of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT A fluorescent lamp according to one embodiment of the invention is illustrated in FIG. I. The lamp has an hermetically sealed, tubular glass envelope'2 containing a suitable rare gas filling, such as for'examplepercent argon. In addition, a charge of mercury is introduced into the envelope, prior to sealing, toyield the necessary mercury vapor pressure for operation of the lamp. On the inside surface of the glass envelope there is a coating of phosphor 4owhich may be, for example, any suitable fluorescent lamp phosphor.

Attached to one end of the glass envelope 2 is a lamp base 6 having a cylindrical shoulder 8, an externally threaded shell 10 secured to shoulder 8 by insulating means and projecting therefrom, and a center contact 12 separated by a body of insulating material 14 from the shell 10. Shoulder 8 is secured to the end of the glass envelope 2 by a suitable basing cement l6, and

the threaded shell 10 and center contact I2 provide a screw-in base compatible with conventional screw-type incandescent lamp sockets.

The lamp contains a single mount structure 18 which is sealed in the end of the envelope to which the base 6 is attached, while the other end of the envelope has a flat or dome seal 20; the mount structure includes a glass flare portion 22 having an exhaust tube 24 and a rigid glass insulating tube 26 projecting from the flare at the base end of the envelope toward the flat or dome seal end of the envelope. A first lead-in wire 28 sealed through the flare 22 supports a first electrode 30 at'the base end of thelamp, and a second electrode 32 is supported by the glass tube 26 at the flat seal end of the envelope. The second electrode 32 is connected to the base by a second lead-in wire 34 which coaxially passes through the length of the glass tube 26 and is sealed through the flare 22.

V To facilitate self-starting in accordance with the invention, an ignition coil 36, which may comprise a coiled-coil of tungsten wire with an electron emissive coating over substantially its entire length, is located within the envelope 2 and connected between the ends of the lead-in wires 28 and 34 disposed therein. The electron emissive coating on coil 36 may be of a conventional type such as a mixture of barium, strontium and calcium carbonates, which are reduced during lamp processing to their oxide forms. Electrode 30 includes a cathode element, which comprises a portion of the ignition coil at the junction 38 of the ignition coil 36 and lead-in wire 28, and an anode element 40 comprising a strip of metal electrically attached to junction 38, such as by welding. In like manner, electrode 32 includes a cathode element, which comprises a portion of the ignition coil at the junction 42 of the ignition coil 36 and the lead-in wire 34, and an anode element 44 comprising a strip of metal electrically attached to juntion 42, such as by welding. The anode elements may be in the form of other configurations, such as discs, suitable for the electron collecting function, and may comprise any of the materials typically employed for anode flags in fluorescent lamps, such as strips of nickel or nickel plated stainless steel.

Electrode 30 is electrically connected to a first terminal of base 6 by lead-in wire 28, which at one end is clamped to the electrode at juntion 38 and at the other end (not shown) may be soldered to the threaded metal shell 10. Electrode 32 is electrically connected to a second terminal of base 6 by the lead-in wire 34, which proceeds from clamped junction 42 through the insulating glass tube 26 and flare 22 to a solder connection (not shown) at center contact 12. When the lamp is ignited, as will be described hereinafter, the are discharge path is formed essentially between juntions 38 and 42 and may be appropriately located by suitably shaping the portion of lead-in wire 28 projecting into the envelope from flare 22, and by forming a bend in the remote end of glass tube 26 supportingjunction 42. The ignition coil 36 connected between junctions 38 and 42 is then suspended away from the arc discharge path between electrodes 30 and 32 by a plurality of support wires 46 projecting from the glass insulating tube 26. To stabilize and support the remote end of the glass tube 26, a resilient wire support structure 48 may be located at the flat seal end of the lamp in engagement with the lamp walls and the bent remote end of the glass tube. Generally, the wire support structure 48 is only required for longer are lengths, such as those described hereinafter in connection with FIG. 3.

The single base fluorescent lamp of FIG. 1 may be mounted in a conventional threaded incandescent lamp socket or a left-hand threaded socket and operated from a standard 60 cycle, I volt AC line source. Alternatively, a single bi-pin base may be used instead of a screw-in incandescent base. The ignition coil 36 shunts the arc and develops the starting voltage required by the lamp. Accordingly, the lamp has an autoignition capability which permits a wide latitude in choice of ballasting. as the ballast need only function as a current regulator, Heretofore, a fluorescent lamp ballast served the dual function of ignition and current regulation. According to one typical application, the ballast for the lamp of FIG. 1 may comprise a simple inductive choke contained within the base of the fixture into which the lamp is mounted.

In operation, a current is established in the lamp ignition coil 36 prior to ignition. The current path commences at the lead-in wire 34 and continues through the glass-to-metal seal in the flare 22, up through the glass insulating tube 26 to the remote end of the mount where it enters the ignition coil 36 atjunction 42. Proceeding through the coil 36, the current path exits at junction 38 and passes out through another glass-tometal seal in flare 22, to end at the other lead-in wire 28.

As previously described, the entire ignition coil is coated with a conventional electron emissive coating reduced to the oxide form. The current established in I the ignition coil raises the oxide coating temperature to an emissive state (e.g., 800900C), at which time an electron cloud encircles the coil along its entire length. The electron cloud is accelerated by the longitudinal electric field generated in the coil by the coil current. The electron cloud is accelerated back and forth along the coil at the frequency of the lamp supply voltage (typically cycles per second), resulting in collisions with mercury and rare gas atoms. The by product of these collisions are excited and ionized atoms which increase very rapidly in number until they are of sufficient quantity to maintain conduction between points 42 and 38 without the aid of the oxide coated ignition coil 36. Once conduction is established in this manner, the voltage between points 42 and 38 will drop as the discharge current increases resulting from the negative volt-ampere characteristic of the discharge. At the same time, the current in the ignition coil will decrease since the coil has a positive volt-ampere characteristic. This will lower the temperature of the coil below the emissive level and the arc current will not have a tendency to originate at points along the coil body. The

only emissive points on the coil during lamp operation are in the proximity ofjunctions 42 and 38, which are heated by the arc current.

The anode elements 44 and 40 serve to increase the efficiency and extend the life of the lamp by functioning as electron collectors during anode half cycle operation. The emissive coil is suspended away from the longitudinal axis of the discharge by the support wires 46 anchored to the glass insulating tube. This refinement further isolates the ignition coil from the are discharge current after the lamp has started. The glass tube 26, therefore, serves a dual function in that it electrically insulates the conducting wire 34 from the plasma and also serves as an anchorage for the ignition coil support wires.

The foregoing description of operation may be more formally expressed as follows. In any type of gas discharge, the breakdown mechanism depends on the development ofa Townsend avalanche across the arc gap. In a conventional dual mount two-electrode lamp, the electron avalanche current, as a function of distance x along the tube, is equal to where i is the electron current emitted from the cathode and a is the probability per unit length for an ionization type collision to occur. From equation (1) it is seen that the electron emission current at the cathode is exponentially amplified in relation to the electrode spacing and a, which is a function of gas, pressure, and electric field. Of course, the total current (positive ions plus electrons) inthe tube does not vary with distance, so that the ion current from anode to cathode must be the mirror image of equation (I). Since the mobility of the positive ions is much less than that of the electrons, the electric field along the lamp must distort to develop the required ion current gradient to mirror that of the electrons. As the avalanche current in the lamp increases, the lamp field with continue to distort increasing in strength at the cathode until the onset of secondary electron emission satisfies the familiar breakdown equation for a self-sustaining discharge,

wi e 1,

where 71' is the secondary emission coefficient, and d is the electrode spacing.

The breakdown mechanism in the single base lamp of FIG. 1 appears to result from the increased field distortion in the lamp associated with the electron emission which occurs along the entire length of the ignition coil 36. An exact quantitative expression of the Townsend avalanche current for this condition, analogous to equation (1), is difficult to obtain for the singleelectrode design because the derivation involves integration of the term e where a is a function of the electric field. For constant-a the expression would be where i /d is the emission current per unit length of ignition coil. Equation (3) does serve to show that an increase in the electron avalanche current will occur relative to a standard lamp and with it an increase in the field distortion at the cathode end of the ignition coil.

Predicted field patterns in a standard fluorescent lamp and a single base lamp (FIG. 1) of equal arc length and the same lamp voltage exhibit the same average field strength for both lamps, but a higher field at the coil terminus of the single base lamp. This higher field at the coil terminus produces a localized breakdown whereby a self-sustaining discharge develops along a small section of the ignition coil. This localized discharge satisfies the condition for self-maintenance as expressed in equation (2), where the terms a and d now assume the values associated with the localized discharge. The ionization by-products of this local breakdown reduce the field strength at this point on the coil and shift it down along the coil where the breakdown process repeats until the discharge jumps the coil and fills the tube.

In summary, the ignition coil 36 performs two functions to aid in starting: (1) the ignition emission along thelength of the coil 36 serves to favorably distort the lamp field above the coil to a degree not attainable in a conventional lamp; (2) the field so generated satisfies locally the condition for a self-sustaining discharge over a small section of the coil 36 which will gradually increase in length until it fills 'the tube. The action of the ignition coil 36 can be likened to an electron emissive internal ground plane. Accordingly, the ignition coil eliminates the requirement that the lamp be mounted next to a conducting surface, thus freeing the lamp from the confines of a metal reflecting fixture.

With respect to design considerations, the resistance of the ignition coil is of particular importance since this will affect the efficiency of lamp operation. This can be seen in FIG. 2 where the V-l characteristic of a typical single base lamp is shown together with a portion of the inductive ballast load line. After ignition, the rms operating point wil be located at point'(V,,, I,,). such The bypass current through the ignition coil is determined by the lamp voltage intercept on the positive sloped such section of the lamp characteristic at point (V 1.). For maximum efficiency it is desirable to reduce the bypass current to a minimum by use of a high resistance coil.

There exists a practical limit, however, on how high this resistance can be since the coil must pass sufficient preheat current at a relatively low voltage to result in an ignition point (V,-, I.) which lies well below the inductive ballast load line. Another reqirement for the ignition coil is that it be able to carry the arc current at its terminal points without overheating.

In lamps made according to FIG. 1, an arc-to-coil current ratio of 3.5:1 has been achieved for an arc current of 350 ma. I have also found it desirable to coat the entire length with emissive material since this will increase the avalanche current considerably and thereby allow lamp starting at a lower voltage.

The impedance of the ballast selected for use with the lamp must be ush that the ballast load line will pass above the ignition point (V,-, 1,) in FIG. 2 and intersect the lamp characteristic at the desired operating point 0 0)' If an inductive choke is used, the required inductance L f 0) (V32 o where L is in henries,fis the line frequency, V is the AC line voltage, and 1,, and V are obtained from FIG. 2.

For purposes of example, one specific implementation of FIG. 1, comprising a 12WT12 single threadedbase fluorescent lamp having an overall length of25 cc. (9.75 in.), an arc length of 18cm. (7 in.) and anenvelope diameter of 3.8 cm. (1.5 in.), exhibited the following performance characteristics when operated from a 60 cycle, I20 volt supply in a fixture employing an inductive choke ballast:

Starting voltage 58 volts Starting current I milliamps Lamp voltage 30 volts Lamp current 450 millitimps Lamp powcr 12.5 watts Arc current 350 milliamps Arc power 9.5 watts Ignition coil current I00 milliumps Ignition coilpowcr 3 watts Lumcns 350 Lumcns per watt 28 The specific lamp construction of FIG. 1, however, is generally suitable only for lamps having an arc length of less than ten inches. For longer length lamps, the electron cloud generated along the oxide coated ignition coil cannot be exicted to a sufficient degree by the coil field to cause the sustained excitation and ionization of fill gas required to provide lamp ignition. In accordance with an alternative embodiment of the invention, this difficulty is overcome by the inclusion of a V- shaped ionization coil in the center of the main ignition coil. This lamp construction is illustrated by the alternative mount structure 18 shown in FIG. 3. As indicated, the V-shaped ionization coil structure may be formed from the ignition coil 36' at approximately the center of the length thereof and supported from the glass insulating tube 26 by projecting 'wires 52, the apex of the V being secured to the glass tube at point 54. The, remainder of the ignition coil 36', except for the two; end portions is suspended linearly between the ends of the insulating tube.

Electrical connections are made to a lamp employing the mount structure of FIG. 3 as described for FIG. 1,

and current is established through the oxide coated ignition coil and V-shaped ionization coil 50 in the same manner described in the operation of the lamp of FIG. 1. An electron cloud in generated along the length of the ignition coil and along the V-shaped ionization coil 50. The coil 36 field accelerates the electron cloud of the main ignition coil 36' at the line frequency rate (e.g., 60 cycles per second), but is ineffective at maintaining sustained excitation and ionization. The field produced in the V-shaped zone, however, is effective in establishing a discharge between the legs of the V- shaped coil structure 50. The discharge initiated in this manner then proceeds to migrate symmetrically along the main oxide coated ignition coil, terminating at juntions 42 and 38, at which point the discharge will fill the tube.

For purposes of example, one specific implementation of a lamp including the mount structure of FIG. 3, comprising a single threaded-base fluorescent lamp having an overall length of about 46 cm. (18 in.), an arc length of 33 cm. (13.4 in.) and an envelope diameter of 3.8 cm. 1.5 in), exhibited the following performance characteristics when operated from a 60 cycle, 120 volt supply in a fixture employing an inductive choke ballast.

Starting voltage 105 volts Starting current l40 milliamps Lamp voltage 50 volts Lamp current 400 milliamps Lump power 18.5 watts Arc current 300 milliamps Arc power l watts Ignition coi l current 100 milliamps Ignition coil power 5 watts Lumens 650 Lumcns per watt 35 Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. For example, tube 26, may be made from insulating materials other than glass, and the lamp may also be operated from a DC supply, an automobile inverter ballast supply, or from a higher frequency AC source. such as the 400 cycle supply employed in aircraft lighting.

What I claim is:

l. A fluorescent lamp comprising: an hermetically sealed, tubular glass envelope; .a phosphor coating on the inside surface of said envelope; mercury and a rare gas contained in said envelope; a lamp base attached to one end of said envelope; and a mount structure sealed in said one end of said envelope and comprising, a first electrode supported at said one end of said envelope, a first lead-in wire electrically connecting said first electrode to a first terminal of said base, a rigid insulating tube within said envelope projecting from said one end of said envelope toward the other end thereof, a second electrode supported by said tube at said other end of the envelope, a second lead-in wire passing through the length of said insulating tube and electrically connecting said second electrode to a second terminal of said base, an ignition coil located within said envelope and electrically connected between said first and second electrodes, said ignition coil having an electron emissive coating over substantially its entire length, and support means projecting from said insulating tube and suspending said ignition coil away from the axis of the arc discharge path between said first and second electrodes.

2. A lamp according to claim 1 wherein said first electrode comprises a portion of said ignition coil at the junction of said ignition coil and said first lead-in wire, and said second electrode comprises a portion of said ignition coil at the junction of said ignition coil and said second lead-in wire.

3. A lamp according to claim 2 wherein each of said first and second electrodes includes a cathode element and an anode element, each cathode element comprising said respective portion of ignition coil at the junction with a respective lead-in wire, and each anode element comprising a piece of metal electrically attached to said coil junction with a respective lead-in wire.

4. A lamp according to claim 3 wherein said insulating tube is glass, said second lead-in wire is located substantially coaxial within said glass tube, said ignition coil comprises a coiled-coil tungsten wire having an electron emissive coating over its'entire length, and each of said anode elements comprises a strip of metal.

5. A lamp according to claim 4 wherein: said emissive coating comprises a mixture of barium, strontium and calcium carbonates reduced to oxide form; and each of said anode elements comprises a strip of nickel or nickel plated stainless steel.

6. A lamp according to claim 1 wherein said tubular glass envelope has a flat seal at the end opposite that to which said base 'is attached.

7. A lamp according to claim 6 wherein said insulating tube is glass, and said second lead-in wire is located substantially coaxial within said glass tube.

8. A lamp according to claim 7 further including a resilient wire support means disposed at the flat seal end of said tubular envelope for supporting the end of said glass tube remote from said base.

9. A lamp according to claim 1 wherein a V-shaped ionization coil structure is formed from said ignition coil and located at approximately the center of said length of ignition coil, said V-shaped coil structure being supported from said insulating tube, and a substantial portion of the remainder of said ignition coil being suspended linearly between the ends of said insulating tube. 

1. A fluorescent lamp comprising: an hermetically sealed, tubular glass envelope; a phosphor coating on the insiDe surface of said envelope; mercury and a rare gas contained in said envelope; a lamp base attached to one end of said envelope; and a mount structure sealed in said one end of said envelope and comprising, a first electrode supported at said one end of said envelope, a first lead-in wire electrically connecting said first electrode to a first terminal of said base, a rigid insulating tube within said envelope projecting from said one end of said envelope toward the other end thereof, a second electrode supported by said tube at said other end of the envelope, a second lead-in wire passing through the length of said insulating tube and electrically connecting said second electrode to a second terminal of said base, an ignition coil located within said envelope and electrically connected between said first and second electrodes, said ignition coil having an electron emissive coating over substantially its entire length, and support means projecting from said insulating tube and suspending said ignition coil away from the axis of the arc discharge path between said first and second electrodes.
 2. A lamp according to claim 1 wherein said first electrode comprises a portion of said ignition coil at the junction of said ignition coil and said first lead-in wire, and said second electrode comprises a portion of said ignition coil at the junction of said ignition coil and said second lead-in wire.
 3. A lamp according to claim 2 wherein each of said first and second electrodes includes a cathode element and an anode element, each cathode element comprising said respective portion of ignition coil at the junction with a respective lead-in wire, and each anode element comprising a piece of metal electrically attached to said coil junction with a respective lead-in wire.
 4. A lamp according to claim 3 wherein said insulating tube is glass, said second lead-in wire is located substantially coaxial within said glass tube, said ignition coil comprises a coiled-coil tungsten wire having an electron emissive coating over its entire length, and each of said anode elements comprises a strip of metal.
 5. A lamp according to claim 4 wherein: said emissive coating comprises a mixture of barium, strontium and calcium carbonates reduced to oxide form; and each of said anode elements comprises a strip of nickel or nickel plated stainless steel.
 6. A lamp according to claim 1 wherein said tubular glass envelope has a flat seal at the end opposite that to which said base is attached.
 7. A lamp according to claim 6 wherein said insulating tube is glass, and said second lead-in wire is located substantially coaxial within said glass tube.
 8. A lamp according to claim 7 further including a resilient wire support means disposed at the flat seal end of said tubular envelope for supporting the end of said glass tube remote from said base.
 9. A lamp according to claim 1 wherein a V-shaped ionization coil structure is formed from said ignition coil and located at approximately the center of said length of ignition coil, said V-shaped coil structure being supported from said insulating tube, and a substantial portion of the remainder of said ignition coil being suspended linearly between the ends of said insulating tube. 